This invention pertains to an improvement in rotary shear shredding, and specifically to an improved system, and to an associated, improved methodology, based upon controlled-feed-rate shredding of material in a rotary shear shredder. More particularly, it concerns such a system and methodology which involve metering the flow of material through the shredding (shearing) zone in such a shredder by variably differentiating, through the making of single-shaft motion adjustments, the relative rotational motions of the usual, two, power-driven, conventionally matched-motion counter-rotating, knife-carrying shafts which, with their respectively carried, circularly-overlapping-sweep knives, define this shredding zone. The phrase of “circularly-overlapping-sweep” associated with these knives refers to the usual shearing circular overlap of the travel circles described by the outer extremities of the knives in the two sets of “shear-overlapping” knives carried by the shafts as the knives and shafts are viewed along their rotational axes.
The terminology “matched-motion”, and the like, herein is intended to refer to the usual matching-speed counter-rotations of the two shaft. The terminology “variably differentiating” the relative rotational motions of such two shafts, and the like, is intended to refer to the making of single-shaft-only relative motion (rotational speed and/or rotational direction) adjustments.
Material-flow metering, in accordance with both a preferred embodiment of the invention system, and a preferred practice of the invention with that system, is carried out effectively throughout the durations of shredding operations, and involves holding the speed and rotational direction of one of the two (two shafts being illustrated herein in the preferred embodiment) shredder shafts, which is variously called herein the selected “main”, or the selected “method-designated main”, shaft, essentially constant while selectively and differentially varying, in relation to the monitored shredding torque load exerted on that “main” shaft, the speed, and under certain circumstances also the direction, of rotation of the other which is variously referred to herein as the selected “controlled”, or “metering”, or the selected “method-designated controlled”, shaft. This differential relative-shaft-motion control (the above-mentioned concept of variable differentiation) is implemented systemically preferably under the influence of an appropriately programmed digital computer so as to achieve, as much as possible, a continuously steady, non-jamming material throughput through the shredder's shredding zone.
The invention proposes both preferred and best-mode, and several modified, systemic embodiments and manners of methodologic practice, each suited to different, specific shredding application needs.
Common to all embodiments and methodologic practices of the invention is the mentioned, single-shaft-only, differential relative-motion (variable differentiation) shaft control—a feature, always associated with the selected “controlled” (or “metering”) shaft, which feature is believed to offer unique and distinctly effective improvements, relative to background-past problems, in the operations of rotary shear shredders.
Heretofore, rotary shear shredders generally shred material which is supplied as input via a gravity feed hopper. Typically a shredder's associated hopper is loaded from a conveyor, a dumper or directly by hand. Different types of process material, and the just-mentioned, typical infeeding methods, directly impact the torque load exerted on the power-driven, rotating-knife-carrying shredder shafts.
These two factors—feed style and material type—cause significant shredder torque demand variations that typically lead to expensive design over-sizing of shredder drives, and to costly revising of shredder-cutting geometry, such that the toughest material to be processed can confidently and correctly be shredded.
As those skilled in the relevant art well know, some process materials are essentially unable to be shredded due their propensity to self-feed. Examples of this are baled aluminum, and stringy materials such as tarps and so-called super-sacks.
As suggested above, the present invention, in each of its herein-described embodiments and manners of operation, all of which feature the above, generally described differential relative-motion shaft control, satisfactorily, and with definitive improvements, takes into account these prior art shear-shredding considerations.
According to a preferred and best-mode embodiment of the invention, what the invention proposes, generally speaking, is a system for the controlled-feed-rate shredding of material in a rotary shear shredder, including:
(1) a pair of spaced, laterally adjacent, nominally matched-motion counter-rotating, power-driven shredder shafts, including, under all shredding operating conditions, a selected main shaft and a selected controlled, or metering, shaft, these shafts carrying sets of confrontingly rotating knives which, with their associated shafts, define between them a shredding zone into which material to be shredded is fed,
(2) a pair of drive motors, each drivingly connected to a different one of the two shafts, each motor being selectively, and individually, speed-variable and rotation-direction reversible, and
(3) operatively associated with the shafts and motors, material feed-rate control structure, including                (a) a torque load sensor at all times operatively connected to the drive motor which is drivingly connected to the selected main shaft, operable effectively to monitor, continuously during shredding, the torque load experienced by that shaft,        (b) a speed and direction controller at all times operatively connected to the drive motor which is drivingly connected to the selected controlled, or metering, shaft, operable to change the rotational speed and the rotational direction of that shaft, and        (c) an algorithmically programmed digital computer operatively connected both to the sensor and to the controller, operable, based upon the selected main shaft torque load monitored by the sensor, and employing the controller in relation to the drive motor which is drivingly connected to the selected controlled shaft, to control selectively, in a manner variably differentiating the relative rotational motions of the two shafts, the rotational speed and, if needed, the rotational direction of the selected controlled shaft in a way effective to achieve a desired, appropriate and controlled, material-shredding feed-rate through the shredding zone.        
In this preferred and best-mode embodiment of the invention, the two shredder shafts and their power-drive motors, are essentially identically sized, and possess essentially the same operational torque-load capacities. Both have the same speed ranges, peak transmitted torques, and overall knife sizes and shapes. The selected “main shaft” runs always at full speed, and with its carried knives does the majority of the shredding. The selected “controlled, or metering, shaft” controls the “main shaft” load by varying its speed, and if needed, its rotational direction. The main shaft torque is monitored, as mentioned, and this monitored torque is used to control the speed and rotating direction of the metering shaft.
Embodiment variations include (1) periodically swapping the roles of the two shafts in such a manner that each shaft becomes, variously and alternately, in one interval of time the selected main shaft, and in another, alternate interval of time the selected controlled (or metering) shaft, and (2) implementing the invention features in a shredder wherein the two shafts and their associated drive motors are differentiated in sizes and working capacities, and wherein the smaller and lower-capacity shaft and associated drive motor always function in the selected, controlled/metering mode of operation.
From one methodologic point of view, and still generally speaking, the invention offers a method for metering the flow of material through the shredding zone in a rotary shear shredder, which zone is defined by confrontingly rotating knives that are carried on a pair of adjacent, power-driven, nominally matched-motion counter-rotating shafts, including holding the speed and rotational direction of one of the shafts essentially constant while selectively changing, in a manner variably differentiating the relative rotational motions of the two shafts, the speed, and under certain circumstances also the direction, of rotation solely of the other shaft.
From another methodologic perspective, the invention proposes a material-feed-rate method for the controlled, through-flow shredding of material fed into the shredding zone in a rotary shear shredder, which zone is defined by confrontingly rotating knives carried on a pair of elongate and parallel, adjacent, nominally counter-rotating, power-driven shafts including, under all operating conditions, a selected, method-designated main shaft and a selected, method-designated controlled shaft. The method steps include (a) monitoring, during shredding, the torque load exerted on the method-designated main shaft, and (b) in response to such monitoring, and in relation to the respective operations of the two shafts in the pair, selectively varying at least one of (1) the speed and (2) the rotational direction of the method-designated controlled shaft in a manner intended to achieve desired, appropriate and controlled, material-feed-rate through the shredding zone.
These and other various features and advantages of the invention will become more fully apparent as the detailed description of it presented below is read in conjunction with the accompanying drawing.